Magnetic disc memory units are widely used in data processing systems because such units have high storage capacity and require relatively short time for read/write heads of a disc memory to access data stored at a given point on the disc in response to a disc memory address supplied to the memory unit. Magnetic discs employed in disc memory units carry data on circular concentric tracks, typically positioned on both sides of the disc. The tracks generally have a width of no more than a few dozen microns. To transduce, i.e., read and write, data on the disc, magnetic heads of the memory units are positioned adjacent opposite faces of the disc, at a distance of a few tenths of a micron.
The magnetic discs are rotatably driven by an electric motor of the disc memory unit at a constant rotational speed. Current memory units frequently include a limited number of discs, i.e., one or two discs, and have a relatively limited storage capacity, on the order of ten to several tens of millions of bytes. Each byte typically includes eight bits, i.e., a binary digit data unit having a value equal to one or zero, as indicated by a magnetic flux transition on a track of the disc. Typically, at least one disc is enclosed in a cartridge that is selectively inserted into and removed from a receptacle of the magnetic disc memory unit. A disc memory unit receptacle normally contains only a single removable cartridge. When a cartridge is immediately inserted into the receptacle as soon as read and/or write operations have been completed on the disc in the initially inserted cartridge. Thus, plural removable cartridges, each containing at least one magnetic disc, are used with a single disc memory unit.
Certain disc memory units contain two magnetic discs, one of which remains permanently inside the disc memory unit; the other disc is contained in a cartridge that is selectively inserted and removed from the disc memory unit receptacle.
Cartridges containing removable magnetic discs have standarized shapes and dimensions, enabling them to be used interchangeably with magnetic disc units of different manufacturers. Thereby, the standarized cartridges are easily inserted into and removed from the receptacles of many different magnetic disc memory units. The cartridges are constructed to protect discs located therein from contamination by dust and other particulate matter during periods while the cartridges are not in use, i.e., while a particular cartridge is not in a magnetic disc memory unit receptacle. The prior art cartridges typically include structure for ventilating the disc while the cartridge is in the disc memory unit receptacle, thereby to insure that the disc remains extremely clean, to increase reliability of data read from the disc. Exemplary of such a cartridge which is selectively inserted into and removed from a receptacle of a magnetic disc memory unit is disclosed in U.S. Pat. No. 4,078,246, commonly owned with the present invention, and entitled "Container For A Magnetic Disc".
The cartridge disclosed in the U.S. Pat. No. 4,078,246 contains a rigid disc having a relatively small diameter. The cartridge is relatively flat, having a height less than one tenth the length or width thereof. The cartridge is inserted into a suitable disc memory unit receptacle. The cartridge includes a side wall having an opening which is normally closed while the cartridge is not in use, i.e., when the cartridge is not in the disc memory unit receptacle. When the cartridge is in the disc memory unit receptacle, magnetic read/write heads of the unit extend through the opening and are moveable relative to recording tracks on the disc. The cartridge includes a mechanism for coupling a hub carrying the disc to a rotary drive mechanism, usually an electric motor, of the disc memory unit.
The cartridge includes rigid, elastically deformable, opposed, generally parallel walls having a tendency to be outwardly convex in a free state. At the center of one of the parallel walls is an internal projection, forming an annular bearing surface facing an inside face of the one wall. The other wall includes an opening coaxial with the center of the one wall. The opening in the other wall is surrounded by an annular bearing surface on the outside face of the other wall. The disc is carried by an annular hub having internal and external flanges positioned to engage the bearing surfaces of the other wall. The axial spacing between the flanges is less than the spacing between the bearing surfaces of the other wall while the other wall is in the free state, whereby when the disc is in an idle state and the parallel walls are flattened an elastic restoring force mechanically holds the disc in proper position. When the cartridge is in the receptacle of the magnetic disc memory and the disc is being driven, the disc is able to turn because the walls are urged toward each other, with a concave configuration. The bearing surfaces and flanges are constructed so that the cartridge is sealed when not in use, thereby protecting the hub carrying the disc and the disc from dust particles. By selecting suitable relative positions and diameters for the flanges, the disc is automatically ventilated during operation in response to a centrifugal effect of air on opposite faces of the disc, to provide cleaning of dust and other particular matter from the disc surface, as well as cooling.
Other removable magnetic disc cartridges having different ventilating systems are known. Such a cartridge is disclosed, for example, in U.S. Pat. No. 3,812,534, entitled "Ventilation Device For Magnetic Disc Unit", and commonly owned with the present application.
A magnetic disc memory unit includes a receptacle for receiving the cartridge. The cartridge disclosed in U.S. Pat. No. 3,812,534 contains at least one magnetic disc and includes first and second lateral openings through which brushes and read/write heads are respectively introduced through walls of the receptacle.
The cartridge of U.S. Pat. No. 3,812,534 includes a conduit for receiving filtered air supplied to the receptacle through an opening in the cartridge. The air supplied to the cartridge leaves the cartridge through the opening in the cartridge through which the heads extend. The filtered air introduced into the cartridge is circulated with the turning disc in response to a centrifugal force produced by the disc rotation. The filtered air has a tendency to escape to the periphery of the disc in response to the centrifugal force. A regulator positioned in a filtered conduit for supplying air to the cartridge provides a constant air flow to the cartridge, which flow is relatively independent of pressure applied to a ventilation conduit intake, to prevent overly rapid clogging of the filter. Thereby, the life of the filter is prolonged, an advantageous feature because disc memories must normally be provided with very high capacity, relatively expensive air filters.
As disclosed, for example, in commonly owned U.S. Pat. No. 4,298,898 data written onto discs enclosed in removable cartridges are separated into adjacent, circular, equal sized segments, with each side or face of the disc being normally divided into several dozen segments. Each segment is divided into two portions of different sizes, such that the larger portion contains data processed or to be processed by a data processing system including the disc memory unit containing the cartridge. The smaller portion contains track identification data used by the data processing system for positioning the read/write magnetic heads of the memory unit relative to the disc tracks. Within each segment, the smaller portion is separated into a number of reference areas. The number of reference areas is equal to the number of tracks, such that each track is associated with a single, separate area. The number of data bits per unit length along the circumference of a disc track is referred to as "longitudinal data density", while "radial density" indicates the number of tracks per unit length measured along the disc diameter.
The current trend in developing magnetic discs is focused particularly on obtaining substantial increases in radial and longitudinal densities. Typically, radial densities are on the order of 350 to 400 tracks per centimeter, i.e., 850 to 1,000 tracks per inch (TPI), while the longitudinal densities are on the order of 2,000 bits per centimeter, i.e., 5,000 bits per inch (bpi).
It is difficult to obtain the same longitudinal and radial densities on removable magnetic discs enclosed in cartridges as on a disc which remains fixed permanently inside a disc memory unit. The removable feature of such cartridge enclosed magnetic discs is a limiting factor on the longitudinal and radial densities thereof because it is very difficult to obtain an adequately clean environment inside of the cartridge. Any cartridge that can not be air tight to the same degree as a disc which remains fixed permanently inside a disc memory unit may, due to variations in prevailing climatic conditions, absorb dust or other foreign particulate materials in varying quantities. Because the cartridge enclosure is separate from the enclosure in which magnetic read/write heads are situated when the cartridge is not inserted in a receptacle of the magnetic disc unit, there is a high probability that a certain amount of contaminated air enters the cartridge when the cartridge is inserted into the receptacle. In other words, air containing foreign particles originating from the disc memory unit enclosure containing the magnetic read/write heads has a tendency to enter the cartridge. Because foreign particulate materials, such as dust, may be as large or larger than the distance separating the magnetic heads and the magnetic coating on the disc, there is a high probability of errors occurring in reading or writing data.
Thereby, to obtain signals having the same spatial resolution as the resolution of magnetic variations on the disc it is necessary to minimize dust and other foreign particulate materials within the cartridge. In addition, it is necessary to eliminate residual dust which may remain in the cartridge after it has been inserted into the disc memory unit receptacle. Reducing contamination from dust and other foreign paticulate materials in the cartridge is difficult to achieve to an adequate degree in self ventilated cartridges, such as described in U.S. Pat. No. 4,078,246 because there frequently remains very minute particles on the disc surface, which particles have dimensions on the order of the space occupied by data bit on the disc.
It has also been found that a ventilation system such as described in U.S. Pat. No. 3,812,534 does not provide an adequate degree of cleanliness inside of the cartridge. In addition, the system disclosed in U.S. Pat. No. 3,812,534 exhausts air through the same opening as through which read/write heads are introduced; the air introduced through the same opening as the opening through which the read/write heads are introduced may disturb the position of the heads relative to the magnetic disc.
It is, accordingly, an object of the present invention to provide a new and improved ventilation system and method for a cartridge containing a removable magnetic disc, wherein contamination by dust or other foreign particles is considerably reduced.
Another object is to provide a new and improved magnetic disc cartridge having provisions for circulating gas against surfaces of the disc to dislodge particulate materials that adhere to the disc while in storage and prevent accumulation of such materials on the disc while in use.